1. Field of the Invention
This invention relates to controllers for reciprocal-type pumps or motors and more particularly to a DC powered circuit for controlling linear type actuators.
2. Description of the Prior Art
Rotational motors using bearings, seals, cams and/or linkages for pumping gases or liquids, or for direct drive of such tools as automatic saws, clippers, or linear actuators for control of machinery are well known.
Pumps of this type are described in prior patents such as U.S. Pat. No. 3,437,044 entitled "Fluid Cooled Double Solenoid Pumping Mechanism", dated Apr. 8, 1969, and U.S. Pat. No. 3,282,219 entitled "Double Acting Solenoid Pump", dated Nov. 1, 1966. Pumps of the type described in these patents are driven by a relay which ultimately energizes two coils. The relays operate much too slowly and have too short a life expectancy to make relay-based pump controllers practical. Other controllers for reciprocating plunger-type pumps presently on the market, such as those which control automotive fuel pumps and refrigeration pumps, control a single coil to move the plunger in one direction and a spring to return the plunger to its initial position. Springs are subject to fatigue failure and cannot be controlled to provide variable pressure or flow.
To overcome the many disadvantages of the pump controllers described above, a reciprocating linear pump controllable by an alternating current-powered solid state circuit has been developed. A pump of this type is described in U.S. Pat. No. 5,085,563 entitled "Reciprocating Pump or Motor", dated Feb. 4, 1992, which is hereby incorporated herein by reference. The unique solid state circuit described in this patent is able to operate pumps at a high speed of operation. However, the solid state circuit described is powered by an alternating current source. Unfortunately, there are many circumstances in which the use of alternating current is impractical or impossible. For example, it is often difficult to provide alternating current to devices which are designed to be mobile. In such cases, it is clearly desirable to provide a circuit capable of being powered by direct current for controlling a linear pump or motor.